This invention pertains to an improved aqueous slurry process for preparing reinforced polymer composites in the absence of flocculant by employing a salt of an ethylene acrylic acid copolymer as the binder. The subject binder is capable of being coagulated or destabilized by adjusting the pH of the aqueous dispersion and therefore, eliminates the need of adding a separate flocculant.
The aqueous slurry process for preparing reinforced polymeric composites is well known in the art. In particular, the generally practiced processes employ wet-laid aqueous techniques with minor modifications to allow for the utilization of polymeric materials. Such procedures and processes are disclosed in U.S. Pat. Nos. 4,426,470 and 4,431,696. Additionally, foreign patents disclose the wet-laid aqueous procedures modified to produce polymeric composites. Such patents include U.K. Pat. No. 1,263,812; French Pat. Publication No. 2,507,123 and European Patent Office Publication No. 0,039,292 Al.
Typically, reinforced polymeric composites are prepared in a wet-laid aqueous procedure consisting of flocculating an aqueous suspension containing the ingredients of the mixture, dewatering the suspension and drying the mat to produce a reinforced polymeric sheet. The ingredients of the aqueous dispersion prior to flocculating generally comprise a binder, a heat fusible organic polymer and a reinforcing material. As explained in U.S. Pat. No. 4,426,470, the typical binders are aqueous colloidal dispersions of substantially water-insoluble organic polymers having anionic or cationic bound charges in an amount sufficient to provide stabilization of the colloid, but insufficient to cause the polymer to be water soluble. Representative organic polymers are natural rubber, and synthetic rubbers such as styrene/butadiene, isoprene and butyl rubbers. Additionally, latexes of a structured core/shell morphology are disclosed where the shell region has bound charges at or near the surface of the particle.
While the binders generally employed have proven to be adequate they require a flocculant or coagulant to destabilize the latex dispersion. Usually, partially hydrolyzed anionic polyacrylamide are employed for cationic systems and cationic modified polyacrylamide and diallyldiethylammonium chloride for anionic systems. It therefore would be desirable to eliminate the necessity to employ a flocculant but not adversely affect the properties of the reinforced polymeric composite.
It has been discovered that the basic procedures and methods for preparing a reinforced polymeric composite can be employed except that by employing a binder of an ionic stabilized aqueous dispersion, such as an ammonium salt of ethylene acrylic acid copolymers, the aqueous dispersion can be destabilized by a pH adjustment. This provides an advantage of eliminating the necessity for a flocculant and, in turn, simplifies the method of preparing a reinforced polymer composite.